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Bad Magnetron in microwave oven?...

J

Jesse Bear

Guest
My over-the-stove microwave oven stopped cooking. Here are some facts:

1) it is over 20 years old

2) Every now and then, it would make a ticking noise and not cook. Turning it off then on again, would clear that problem

3) It now goes through the motions of cooking, and sounds normal, but it doesn\'t cook.

4) The capacitor, diode and transformer appear to be OK. Capacitance is within spec, meter reads about 10Megohms (internal bleeder). Diode conducts in one direction only. Measured about 3KV DC between case ground and magnetron (Yes, I have a high voltage probe and know how to use it - I used to work on 50KV power supplies).

5) Magnetron measures almost zero ohms across filament and open circuit from filament to ground, which all I\'ve read says that\'s a \"good\"
magnetron, but the oven simply does not heat.

So, with all that said - good cap, good diode, 3KVDC at the magnetron - what\'s going on? *Almost* every fiber of my being says \"MAGNETRON,\" but am I missing something? I would truly like to get this done and back on the wall.
Thanks.
 
J

John Robertson

Guest
On 2021/12/05 9:17 a.m., Jesse Bear wrote:
My over-the-stove microwave oven stopped cooking. Here are some facts:

1) it is over 20 years old

2) Every now and then, it would make a ticking noise and not cook. Turning it off then on again, would clear that problem

3) It now goes through the motions of cooking, and sounds normal, but it doesn\'t cook.

4) The capacitor, diode and transformer appear to be OK. Capacitance is within spec, meter reads about 10Megohms (internal bleeder). Diode conducts in one direction only. Measured about 3KV DC between case ground and magnetron (Yes, I have a high voltage probe and know how to use it - I used to work on 50KV power supplies).

5) Magnetron measures almost zero ohms across filament and open circuit from filament to ground, which all I\'ve read says that\'s a \"good\"
magnetron, but the oven simply does not heat.

So, with all that said - good cap, good diode, 3KVDC at the magnetron - what\'s going on? *Almost* every fiber of my being says \"MAGNETRON,\" but am I missing something? I would truly like to get this done and back on the wall.
Thanks.
I bought out a Radio/TV/Microwave distributor (Main Electronics -
Vancouver, BC) and have some boxes of NOS microwave parts including
Magnetrons.

If you have a part number I may be able to help you...if you can\'t find
it elsewhere.

As for testing - for that I would suggest seeing if you can find a
service manual which should provide you with voltages needed to verify
the power supply is running OK.

Try this repair resource:

http://repairfaq.cis.upenn.edu/sam/micfaq.htm

John :-#)#

--
(Please post followups or tech inquiries to the USENET newsgroup)
John\'s Jukes Ltd.
MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
(604)872-5757 (Pinballs, Jukes, Video Games)
www.flippers.com
\"Old pinballers never die, they just flip out.\"
 
T

tschw...@aol.com

Guest
Have you checked the door interlock switches?

I had one that was misadjusted on a brand new microwave. It pretended to cook but no juice.
 
L

legg

Guest
On Sun, 5 Dec 2021 16:48:17 -0800 (PST), \"tschw...@aol.com\"
<tschw10117@aol.com> wrote:

Have you checked the door interlock switches?

I had one that was misadjusted on a brand new microwave. It pretended to cook but no juice.
You wouldn\'t find an interlock switch in the 3KV rail.

RL
 
J

John Robertson

Guest
On 2021/12/06 4:36 a.m., legg wrote:
On Sun, 5 Dec 2021 16:48:17 -0800 (PST), \"tschw...@aol.com\"
tschw10117@aol.com> wrote:

Have you checked the door interlock switches?

I had one that was misadjusted on a brand new microwave. It pretended to cook but no juice.

You wouldn\'t find an interlock switch in the 3KV rail.

RL
No response from the OP to any suggestions...

John :-#(#

--
(Please post followups or tech inquiries to the USENET newsgroup)
John\'s Jukes Ltd.
MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
(604)872-5757 (Pinballs, Jukes, Video Games)
www.flippers.com
\"Old pinballers never die, they just flip out.\"
 
F

Fax Machine

Guest
On Monday, December 6, 2021 at 12:21:29 PM UTC-5, John Robertson wrote:
On 2021/12/06 4:36 a.m., legg wrote:
On Sun, 5 Dec 2021 16:48:17 -0800 (PST), \"tschw...@aol.com\"
tschw...@aol.com> wrote:

Have you checked the door interlock switches?

I had one that was misadjusted on a brand new microwave. It pretended to cook but no juice.

You wouldn\'t find an interlock switch in the 3KV rail.

RL

No response from the OP to any suggestions...

John :-#(#
--
(Please post followups or tech inquiries to the USENET newsgroup)
John\'s Jukes Ltd.
MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
(604)872-5757 (Pinballs, Jukes, Video Games)
www.flippers.com
\"Old pinballers never die, they just flip out.\"
Oh dear, I didn\'t mean to make you think I wasn\'t responding.

1) I had already looked at http://repairfaq.cis.upenn.edu/sam/micfaq.htm and it didn\'t contain any more information about testing magnetrons than I had already completed. According to those tests (continuity between the filament pins and open circuit from filament pins to case), I have a good magnetron [but I still have no heat].

2) This cannot be a door interlock problem because I do get 3KVDC at the magnetron. Had this been an interlock problem, there would be no high voltage.. Also as legg wrote, there is no way that there would be a door switch interrupting the 3KV.

I appreciate that you have parts available, but you\'re a million miles away (OK, a few thousand), and across the border from the US. By the time shipping was taken care of, \"Cheap\" would become \"EXPENSIVE,\" and the cost really isn\'t the big thing here - I need to get this back on the wall (and working) sooner rather than later. I really do appreciate it, though - I have been lamenting the fact that there are no longer appliance \"graveyards\" anymore - just like car junk yards, there\'s no place of which I am aware to scrounge.

I believe that at this point, I\'ll just shop (more locally) for a magnetron and see how it goes. I will report back here when I know more.

Thanks folks.
 
P

Peter W.

Guest
That a magnetron tube tests \"OK\" with a VOM is not necessarily indicative of its fitness under actual load. A VOM on the OHMS setting puts out, on a good day, downhill, with a tailwind - perhaps 9 volts or so. Mostly far less.. Actual in-use voltage may cause intermittent behavior such as you have observed, until the device finally just crapped out.

Peter Wieck
Melrose Park, PA
 
T

tschw...@aol.com

Guest
On Monday, December 6, 2021 at 6:39:15 AM UTC-6, legg wrote:
On Sun, 5 Dec 2021 16:48:17 -0800 (PST), \"tschw...@aol.com\"
tschw...@aol.com> wrote:

Have you checked the door interlock switches?

I had one that was misadjusted on a brand new microwave. It pretended to cook but no juice.
You wouldn\'t find an interlock switch in the 3KV rail.

RL
Sorry I missed the part about the 3K being present. Of course I am aware that the interlock would not be interrupting the 3KV but it does form an input for your control board.
3KV is about the minimum operating voltage for a magnetron. Perhaps your well-aged magnetron is no longer reliably operating at 3KV. Before you invest in a replacement part, price out a new oven. We recently bought new appliances for a kitchen remodel and the very nice new microwave oven was the least expensive item and has a host of features that are likely absent from your old unit. Also much lighter and easy to install.
 
J

John Robertson

Guest
On 2021/12/06 10:32 a.m., Fax Machine wrote:
On Monday, December 6, 2021 at 12:21:29 PM UTC-5, John Robertson wrote:
On 2021/12/06 4:36 a.m., legg wrote:
On Sun, 5 Dec 2021 16:48:17 -0800 (PST), \"tschw...@aol.com\"
tschw...@aol.com> wrote:

Have you checked the door interlock switches?

I had one that was misadjusted on a brand new microwave. It pretended to cook but no juice.

You wouldn\'t find an interlock switch in the 3KV rail.

RL

No response from the OP to any suggestions...

John :-#(#
--
(Please post followups or tech inquiries to the USENET newsgroup)
John\'s Jukes Ltd.
MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
(604)872-5757 (Pinballs, Jukes, Video Games)
www.flippers.com
\"Old pinballers never die, they just flip out.\"

Oh dear, I didn\'t mean to make you think I wasn\'t responding.

1) I had already looked at http://repairfaq.cis.upenn.edu/sam/micfaq.htm and it didn\'t contain any more information about testing magnetrons than I had already completed. According to those tests (continuity between the filament pins and open circuit from filament pins to case), I have a good magnetron [but I still have no heat].

2) This cannot be a door interlock problem because I do get 3KVDC at the magnetron. Had this been an interlock problem, there would be no high voltage. Also as legg wrote, there is no way that there would be a door switch interrupting the 3KV.

I appreciate that you have parts available, but you\'re a million miles away (OK, a few thousand), and across the border from the US. By the time shipping was taken care of, \"Cheap\" would become \"EXPENSIVE,\" and the cost really isn\'t the big thing here - I need to get this back on the wall (and working) sooner rather than later. I really do appreciate it, though - I have been lamenting the fact that there are no longer appliance \"graveyards\" anymore - just like car junk yards, there\'s no place of which I am aware to scrounge.

I believe that at this point, I\'ll just shop (more locally) for a magnetron and see how it goes. I will report back here when I know more.

Thanks folks.
Shipping isn\'t that bad (estimate $25USD or so to USA), but I suspect a
replacement part and shipping will likely cost more than a new unit. Sad
as that may be when one likes to fix things!
Mind you I collect old battery radios from the 1920s - and a modern
radio doing the same thing might cost all of $10. One can\'t really put a
price on the joys of tinkering!

John :-#)#

--
(Please post followups or tech inquiries to the USENET newsgroup)
John\'s Jukes Ltd.
MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
(604)872-5757 (Pinballs, Jukes, Video Games)
www.flippers.com
\"Old pinballers never die, they just flip out.\"
 
F

Fax Machine

Guest
On Tuesday, December 7, 2021 at 12:31:58 PM UTC-5, John Robertson wrote:
On 2021/12/06 10:32 a.m., Fax Machine wrote:
On Monday, December 6, 2021 at 12:21:29 PM UTC-5, John Robertson wrote:
On 2021/12/06 4:36 a.m., legg wrote:
On Sun, 5 Dec 2021 16:48:17 -0800 (PST), \"tschw...@aol.com\"
tschw...@aol.com> wrote:

Have you checked the door interlock switches?

I had one that was misadjusted on a brand new microwave. It pretended to cook but no juice.

You wouldn\'t find an interlock switch in the 3KV rail.

RL

No response from the OP to any suggestions...

John :-#(#
--
(Please post followups or tech inquiries to the USENET newsgroup)
John\'s Jukes Ltd.
MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
(604)872-5757 (Pinballs, Jukes, Video Games)
www.flippers.com
\"Old pinballers never die, they just flip out.\"

Oh dear, I didn\'t mean to make you think I wasn\'t responding.

1) I had already looked at http://repairfaq.cis.upenn.edu/sam/micfaq.htm and it didn\'t contain any more information about testing magnetrons than I had already completed. According to those tests (continuity between the filament pins and open circuit from filament pins to case), I have a good magnetron [but I still have no heat].

2) This cannot be a door interlock problem because I do get 3KVDC at the magnetron. Had this been an interlock problem, there would be no high voltage. Also as legg wrote, there is no way that there would be a door switch interrupting the 3KV.

I appreciate that you have parts available, but you\'re a million miles away (OK, a few thousand), and across the border from the US. By the time shipping was taken care of, \"Cheap\" would become \"EXPENSIVE,\" and the cost really isn\'t the big thing here - I need to get this back on the wall (and working) sooner rather than later. I really do appreciate it, though - I have been lamenting the fact that there are no longer appliance \"graveyards\" anymore - just like car junk yards, there\'s no place of which I am aware to scrounge.

I believe that at this point, I\'ll just shop (more locally) for a magnetron and see how it goes. I will report back here when I know more.

Thanks folks.

Shipping isn\'t that bad (estimate $25USD or so to USA), but I suspect a
replacement part and shipping will likely cost more than a new unit. Sad
as that may be when one likes to fix things!
Mind you I collect old battery radios from the 1920s - and a modern
radio doing the same thing might cost all of $10. One can\'t really put a
price on the joys of tinkering!

John :-#)#
--
(Please post followups or tech inquiries to the USENET newsgroup)
John\'s Jukes Ltd.
MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
(604)872-5757 (Pinballs, Jukes, Video Games)
www.flippers.com
\"Old pinballers never die, they just flip out.\"
Amen to the joys of tinkering. I used to think that opening a tinker shop would be fun, but the reality of the throw away society put a stop to that. I know that there are some makerspaces (maybe also schools and libraries) that have fixit events, where you bring your busted toaster or whatever and it becomes a group project to fix them up. I do like that concept.

I am currently awaiting delivery (today) of a replacement magnetron. Hopefully I\'ll have results before the day is done.
 
F

Fax Machine

Guest
On Tuesday, December 7, 2021 at 11:45:05 AM UTC-5, tschw...@aol.com wrote:
On Monday, December 6, 2021 at 6:39:15 AM UTC-6, legg wrote:
On Sun, 5 Dec 2021 16:48:17 -0800 (PST), \"tschw...@aol.com\"
tschw...@aol.com> wrote:

Have you checked the door interlock switches?

I had one that was misadjusted on a brand new microwave. It pretended to cook but no juice.
You wouldn\'t find an interlock switch in the 3KV rail.

RL
Sorry I missed the part about the 3K being present. Of course I am aware that the interlock would not be interrupting the 3KV but it does form an input for your control board.

3KV is about the minimum operating voltage for a magnetron. Perhaps your well-aged magnetron is no longer reliably operating at 3KV. Before you invest in a replacement part, price out a new oven. We recently bought new appliances for a kitchen remodel and the very nice new microwave oven was the least expensive item and has a host of features that are likely absent from your old unit. Also much lighter and easy to install.
New magnetron should be here today - for better or worse, at least there will be a definitive answer. I really don\'t want to buy a new microwave. Yes, they are not *that* expensive, but they *are* several times the cost of a magnetron. Also, hanging this thing back on the wall is literally a one-minute project. If it takes any longer, that means something has gone terribly wrong. A new oven would mean a new mounting plate and at best, that\'s way more work.
 
J

Jesse Bear

Guest
On Monday, December 6, 2021 at 1:32:52 PM UTC-5, Fax Machine wrote:
On Monday, December 6, 2021 at 12:21:29 PM UTC-5, John Robertson wrote:
On 2021/12/06 4:36 a.m., legg wrote:
On Sun, 5 Dec 2021 16:48:17 -0800 (PST), \"tschw...@aol.com\"
tschw...@aol.com> wrote:

Have you checked the door interlock switches?

I had one that was misadjusted on a brand new microwave. It pretended to cook but no juice.

You wouldn\'t find an interlock switch in the 3KV rail.

RL

No response from the OP to any suggestions...

John :-#(#
--
(Please post followups or tech inquiries to the USENET newsgroup)
John\'s Jukes Ltd.
MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
(604)872-5757 (Pinballs, Jukes, Video Games)
www.flippers.com
\"Old pinballers never die, they just flip out.\"
Oh dear, I didn\'t mean to make you think I wasn\'t responding.

1) I had already looked at http://repairfaq.cis.upenn.edu/sam/micfaq.htm and it didn\'t contain any more information about testing magnetrons than I had already completed. According to those tests (continuity between the filament pins and open circuit from filament pins to case), I have a good magnetron [but I still have no heat].

2) This cannot be a door interlock problem because I do get 3KVDC at the magnetron. Had this been an interlock problem, there would be no high voltage. Also as legg wrote, there is no way that there would be a door switch interrupting the 3KV.

I appreciate that you have parts available, but you\'re a million miles away (OK, a few thousand), and across the border from the US. By the time shipping was taken care of, \"Cheap\" would become \"EXPENSIVE,\" and the cost really isn\'t the big thing here - I need to get this back on the wall (and working) sooner rather than later. I really do appreciate it, though - I have been lamenting the fact that there are no longer appliance \"graveyards\" anymore - just like car junk yards, there\'s no place of which I am aware to scrounge.

I believe that at this point, I\'ll just shop (more locally) for a magnetron and see how it goes. I will report back here when I know more.

Thanks folks.
Success! New Magnetron { https://www.amazon.com/gp/product/B005DIS2IG/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1 } Fifty bucks, and all that\'s left now is to screw the case back on and hang it up. Thanks for all your input!
 
J

Jesse Bear

Guest
On Tuesday, December 7, 2021 at 2:00:22 PM UTC-5, Fax Machine wrote:
On Tuesday, December 7, 2021 at 12:31:58 PM UTC-5, John Robertson wrote:
On 2021/12/06 10:32 a.m., Fax Machine wrote:
On Monday, December 6, 2021 at 12:21:29 PM UTC-5, John Robertson wrote:
On 2021/12/06 4:36 a.m., legg wrote:
On Sun, 5 Dec 2021 16:48:17 -0800 (PST), \"tschw...@aol.com\"
tschw...@aol.com> wrote:

Have you checked the door interlock switches?

I had one that was misadjusted on a brand new microwave. It pretended to cook but no juice.

You wouldn\'t find an interlock switch in the 3KV rail.

RL

No response from the OP to any suggestions...

John :-#(#
--
(Please post followups or tech inquiries to the USENET newsgroup)
John\'s Jukes Ltd.
MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
(604)872-5757 (Pinballs, Jukes, Video Games)
www.flippers.com
\"Old pinballers never die, they just flip out.\"

Oh dear, I didn\'t mean to make you think I wasn\'t responding.

1) I had already looked at http://repairfaq.cis.upenn.edu/sam/micfaq.htm and it didn\'t contain any more information about testing magnetrons than I had already completed. According to those tests (continuity between the filament pins and open circuit from filament pins to case), I have a good magnetron [but I still have no heat].

2) This cannot be a door interlock problem because I do get 3KVDC at the magnetron. Had this been an interlock problem, there would be no high voltage. Also as legg wrote, there is no way that there would be a door switch interrupting the 3KV.

I appreciate that you have parts available, but you\'re a million miles away (OK, a few thousand), and across the border from the US. By the time shipping was taken care of, \"Cheap\" would become \"EXPENSIVE,\" and the cost really isn\'t the big thing here - I need to get this back on the wall (and working) sooner rather than later. I really do appreciate it, though - I have been lamenting the fact that there are no longer appliance \"graveyards\" anymore - just like car junk yards, there\'s no place of which I am aware to scrounge.

I believe that at this point, I\'ll just shop (more locally) for a magnetron and see how it goes. I will report back here when I know more.

Thanks folks.

Shipping isn\'t that bad (estimate $25USD or so to USA), but I suspect a
replacement part and shipping will likely cost more than a new unit. Sad
as that may be when one likes to fix things!
Mind you I collect old battery radios from the 1920s - and a modern
radio doing the same thing might cost all of $10. One can\'t really put a
price on the joys of tinkering!

John :-#)#
--
(Please post followups or tech inquiries to the USENET newsgroup)
John\'s Jukes Ltd.
MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
(604)872-5757 (Pinballs, Jukes, Video Games)
www.flippers.com
\"Old pinballers never die, they just flip out.\"
Amen to the joys of tinkering. I used to think that opening a tinker shop would be fun, but the reality of the throw away society put a stop to that.. I know that there are some makerspaces (maybe also schools and libraries) that have fixit events, where you bring your busted toaster or whatever and it becomes a group project to fix them up. I do like that concept.

I am currently awaiting delivery (today) of a replacement magnetron. Hopefully I\'ll have results before the day is done.
Success! New Magnetron { https://www.amazon.com/gp/product/B005DIS2IG/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1 } Fifty bucks, and all that\'s left now is to screw the case back on and hang it up. Thanks for all your input!
 
J

Jesse Bear

Guest
On Tuesday, December 7, 2021 at 2:05:58 PM UTC-5, Fax Machine wrote:
On Tuesday, December 7, 2021 at 11:45:05 AM UTC-5, tschw...@aol.com wrote:
On Monday, December 6, 2021 at 6:39:15 AM UTC-6, legg wrote:
On Sun, 5 Dec 2021 16:48:17 -0800 (PST), \"tschw...@aol.com\"
tschw...@aol.com> wrote:

Have you checked the door interlock switches?

I had one that was misadjusted on a brand new microwave. It pretended to cook but no juice.
You wouldn\'t find an interlock switch in the 3KV rail.

RL
Sorry I missed the part about the 3K being present. Of course I am aware that the interlock would not be interrupting the 3KV but it does form an input for your control board.

3KV is about the minimum operating voltage for a magnetron. Perhaps your well-aged magnetron is no longer reliably operating at 3KV. Before you invest in a replacement part, price out a new oven. We recently bought new appliances for a kitchen remodel and the very nice new microwave oven was the least expensive item and has a host of features that are likely absent from your old unit. Also much lighter and easy to install.
New magnetron should be here today - for better or worse, at least there will be a definitive answer. I really don\'t want to buy a new microwave. Yes, they are not *that* expensive, but they *are* several times the cost of a magnetron. Also, hanging this thing back on the wall is literally a one-minute project. If it takes any longer, that means something has gone terribly wrong. A new oven would mean a new mounting plate and at best, that\'s way more work.
Success! New Magnetron { https://www.amazon.com/gp/product/B005DIS2IG/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1 } Fifty bucks, and all that\'s left now is to screw the case back on and hang it up. Thanks for all your input!
 
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